The present invention relates to a back-up power tong of the type commonly used in oil fields for use with an additional power tong in the making up and breaking out of threaded connections between drill pipes, casing, tubing, and the like.
The use of power tongs in making up or breaking out a drill string or casing section is well known and is now commonplace. Typically, when using such power tongs the conventional rig tongs are utilized to hold the lowermost section of the pipe joint being operated upon. However, only recently extremely high-torque power tongs have become available and, when applying such extremely high torques to a pipe joint or the like, the conventional rig tongs which are not powered are generally very large and cumbersome in order to be strong enough to withstand the high torques involved. Additionally, where a power back-up tong is to be utilized in a high-torque situation, it is desirable that the tongs be constructed in such a way that the power tongs may be placed on the pipe joint as close to the back-up tong as possible. This is especially true when operating with drill pipe, since only the pin and box are of special quality materials and it is at these surfaces that the heads of the two units must operate.
In utilizing a back-up tong with a power tong, it is also advantageous to ascertain the relative torque between the two units during the making up process, hence it is beneficial to provide the units with some degree of mutual freedom, so that a relative torque measurement may be made therebetween. Occasionally the situation arises in the drilling of a well that, during the makeup or breakout operation, the drill string is not held firmly by the collars or slips in the rotary table of the drilling platform and the drill string will therefore begin to slip down into the hole. If this occurs when using conventional back-up tongs, the tongs may be damaged severely since they will be pulled loose from the rig and smashed down against the drill platform floor.